Over one million new chronic wounds develop in the United States each year with estimated treatment costs of $7 billion. Scores of new wound healing products are developed annually, yet wounds continue to be a significant public health problem as our population ages and as rates of diabetes mellitus increase. Wounds can be conceptualized as defects in protective skin coverage. Without this physiological barrier, wounds desiccate and are invaded by microorganisms leading to potential infection, with progressive tissue and fluid loss. The inability to heal lower extremity wounds often leads to amputation. There are several etiologies for chronic wounds, including trauma, burns, radiation, venous stasis, chronic infection, and systemic diseases such as diabetes. Current methods for improving wound healing emphasize effective drainage, prevention of infection, reduction of inflammation and minimization of tissue and fluid loss.
Most chronic wounds are characterized by a loss of cells and connective tissue matrix from at least the outer layer of skin (epidermis) and often also from the lower layer of skin (dermis) and deeper structures such as fat, muscle and bone. Closure of large wounds requires the production billions of cells, nutrition through a vascular network and mechanical strength from proteins and glycosaminoglycans present in a nascent extracellular matrix (ECM). To date, most research on wound healing acceleration has focused on soluble growth factors (i.e. FGF, PDGF, TGF-β, VEGF) that naturally stimulate cell proliferation, migration, ECM deposition and angiogenesis. However, the application of cytokines to wounds remains difficult because of the complex, concerted interaction between these factors and their very short half-life in vivo. Moreover, soluble chemicals alone fail to provide structural guidance to rebuild the tissue architecture.
Mechanical forces are well known to have a fundamental role in biologic systems. In development, forces of developing muscles affect bone formation. In addition the application of mechanical forces has been an important adjunct to surgery. Distraction osteogenesis allows gradual lengthening of bone. Tissue expansion allows gradual lengthening of soft tissues, including nerves and blood vessels. Tension wound-approximation devices close wounds over time. Application of sub-atmospheric pressure to wounds has been shown to increase the vascular supply within the wound and to accelerate healing. All of the above forces are directed at the wound in a single dimension and applied evenly over large areas (greater than 1 cm2).